Innate defense against HIV Infection of CD4+ chemokine co-receptor+ targets by HIV is aided by the proficiency of HIV in eliminating or neutralizing host cell-derived defensive molecules. Among these innate protective molecules, a family of intracellular apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like (APOBEC) cytidine deaminases is constitutively expressed, but inactivated by HIV viral infectivity factor. Recently, we demonstrated that type I Interferon (IFN&#945;), a cytokine with multiple functions in innate and adaptive immunity and a potent inhibitor of HIV in vitro and in vivo, exerts its anti-viral activity, in part, by inducing endogenous APOBEC3 family members. The ability of IFN&#945;to augment cytidine deaminases offered the possibility that the balance between virus and target cell might be altered in favor of the host. Further characterization of transcriptional profiles induced by IFN&#945;using microarrays to identify and dissociate retroviral inhibitors from associated IFN toxicities, revealed multiple molecules with suspected anti-viral activity, including IL-27. To establish whether IFN&#945;toxicity might be sidestepped through the use of downstream IL-27 against HIV, we examined whether IL-27 directly regulated cytidine deaminases. Although IL-27 induces APOBECs, it does so in a delayed fashion. Dissecting the underlying regulatory events uncovered an initial IL-27-dependent induction of IFN&#945;and/or IFN&#946;, which in turn, induces APOBEC3, inhibited by IFN&#945;/&#946;receptor blockade. In addition to macrophages, the IL-27-IFN&#945;connection is operative in CD4+ T cells, consistent with an IFN&#945;-dependent pathway underlying host cell defense to HIV. Although the anti-HIV effects of IFN&#945;have been demonstrated, efficacy and safety in untreated subjects infected with only HIV was unknown. Therefore, untreated HIV-infected volunteers without viral hepatitis were treated with pegylated IFN&#945;2a for 12 weeks and changes in HIV RNA, CD4 counts, pharmacokinetics, pharmacodynamic measurements of 2,5 oligoadenylate synthetase (OAS) activity, induction of IFN-inducible genes (IFIG) and lymphoproliferative responses were measured. Based on these clinical studies, peg-IFN&#945;2a has significant anti-viral activity in HIV-monoinfected patients and this anti-HIV effect correlated with OAS protein and IFIG induction. In ongoing studies, we are defining the mechanisms of reduced viral burden by evaluating specific IFIG and their contribution to inhibition of HIV, including APOBEC, BST/tetherin, TRIM22 and others implicated in in vitro studies. IFN&#945;therapy reduces viral burden in HIV infected individuals, but this cytokine can also lead to immune dysfunction and toxicities, limiting its utility. Through detailed mapping of IFN receptor (IFNAR) binding sites and generation of IFN&#945;hybrids and mutants with structural changes in helix C that influence receptor interactions, the ability to limit retroviral replication can be altered. Our data show a differential ability of IFN&#945;constructs to block HIV replication when compared to the wildtype IFN&#945;molecule, and the directional magnitude of HIV inhibition correlated with levels of APOBEC3 gene expression. Subsequent to binding with distinct affinities to IFNAR, the mutants trigger discreet or shared intracellular signaling pathways (Jak/Stat/PI3K/NF&#954;B) leading to antiviral regulation that may be dissociated from underlying toxic effects, exemplified by indoleamine 2,3-dioxygenase (IDO). By exploring the structure and function of IFN&#945;relative to its ability to induce APOBEC and other anti-viral molecules, it may become possible to design novel IFN-related molecules, which preserve its beneficial roles in anti-viral and anti-tumor activity while reducing toxicities. Based on these promising studies, we plan to explore primate studies to evaluate whether selected mutants exhibit similar optimal APOBEC to IDO ratio activity in pre-clinical studies, with potential implications for intervention in HIV infection of humans. In earlier studies, we demonstrated that a synthetic triterpenoid and PPAR&#947;ligand, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), known to influence p21 kinase inhibitor expression (linked to viral life cycle), suppressed viral replication in macrophages and PBMC. A methyl ester derivative of CDDO (CDDO-Me), which is uniquely orally bioavailable, does not have significant toxicities, and since this methyl ester derivative targets tissues, rather than blood, we have focused on defining its ability to inhibit HIV in tonsil tissue-derived CD4+ HIV target cells. Among the potential mechanisms by which CDDO-Me inhibits HIV infection in tonsil cells is through induction of hemoxygenase (HO-1), recently shown to interfere with HIV infection, as well as induction of antiviral type I IFN. These and other pathways will be further evaluated in our in vitro studies as well as in patient populations. As anti-retroviral therapy is often characterized by high toxicity and frequently results in the emergence of drug resistant virus strains, the identification of new anti-viral agents targeting host cell molecules that can be used independently or in conjunction with current anti-viral drugs may provide additional resources in the treatment of HIV infection.